I find shooting through glass on an angle helps, avoids getting flashes in the shot, a slight trade off in clarity though...
I always make sure I have a completely empty memory card, full batteries (with back ups) before I go as it is a trial and error exercise...
Also be prepared for people to look at you weird when you take a picture of an interesting tank feature or a plain looking fish, you can almost read the other peoples thoughts. "Why isn't he taking a photo of that big, pretty shark swimming right past us"...